1. Field of The Invention
The present invention relates generally to a shift timing control arrangement for an automotive automatic transmission. Specifically, the invention relates to a shift timing control arrangement in which oil temperature and viscosity are considered in determining shift timing.
2. Description of The Prior Art
Shift control arrangements for automatic transmissions are well known in which shift timing for establishing a given gear ratio is controlled by driving means for operating solenoids for engaging various frictional elements of the automatic transmission.
One such conventional shift control arrangement is disclosed in Japanese Patent Application First Publication No. 1-188750.
According to the system disclosed in the above-mentioned publication, a rotational speed of an input shaft and a rotational speed of an output shaft of the automatic transmission are detected and compared for determining a gear ratio. A preset ratio for each kind of shift is changed to an actual ratio after shifting by switching means for switching the state ON * OFF state of a solenoid.
According to the above control, shift timing control is carried out based on a present gear ratio, thus an appropriate shift timing can be obtained, even when non-consecutive, or engine braking type shifting is carried out.
However, the above described conventional shift timing control arrangement does not consider a present fluid temperature and viscosity. Since the viscosity of the transmission fluid can change considerably according to temperature, a timing of engagement of frictional elements effected by a hydraulic circuit of the automatic transmission can vary widely, and, since such considerations are not utilized in conventional shift timing control, shift shock, engine overrevving, and a degraded shift smoothness can result.
Thus it has been required to provide a shift control arrangement for an automatic transmission which can assure smooth shift characteristics regardless of a fluid temperature or viscosity.